To enable multi-user mode within QuickBooks, Intuit recommends that you enable the "Host Multi-User Access" feature:
1. Open QuickBooks and go to File / Utilities / Host Multi-User Access
2. Answer "Yes"
3. You'll receive a window that says "Your company file is now set up for multiple users, but you need to do one more thing." - Press OK
4. Log into your company file
5. Click on File, and you should now be able to choose "Switch to Multi-user Mode" (if it says "Switch to single-user mode, that means the company file is already in multi-user mode).
Enabling Host Multi-User Access will also correct the following errors:
• "We're sorry. QuickBooks encountered a problem. We recommend you download the QuickBooks Company File Diagnostic Tool, which can access and possibly correct the problem. Error codes: (-6144, -82)"
• "QuickBooks is unable to open this company file. It may have been opened by another user. You should ask that user to switch to multi-user mode so you can both use the company file at the same time. The file could also be located in a read-only network folder. If it is, ask your system administrator to make the file accessible. Error codes: (-6073, -99001)"